The data confirms a warning last week by European Central Bank chief Mario Draghi that growth in the 19-country single currency bloc was reaching "some moderation" in the face of protectionist dangers.
Economic growth in the eurozone hit 0.4 percent in the January to March period, below the 0.7 percent in the previous quarter, the EU's Eurostat statistics agency said.
On a year-to-year basis, economic growth in the eurozone reached 2.5 percent, lower than the 2.8 percent in the previous quarter but still far ahead of the 1.8 percent reached in 2016.
The figures, after a bumper 2017, add to a slew of economic data in recent months that suggested the single currency area has lost momentum.
Last week France posted a steep drop in growth from 0.7 percent to 0.3 percent in the quarter, with Italy flat at 0.3 percent.
Unemployment in the 19-country single currency area meanwhile remained stable at 8.5 percent in March, its lowest level since December 2008, Eurostat said.
